1. Field of the Invention
The present disclosure relates to a hardness tester.
2. Description of Related Art
As a material tester, a hardness tester is conventionally known in which forms an indentation by pressing an indenter column into a surface of a sample, the indenter column having an indenter on a foremost end thereof, and then measures a depth of the formed indentation (displacement amount of the indenter) with a displacement gauge. Using a relationship between the displacement amount and a test force applied to the indenter, the hardness tester measures physical property values of the sample, such as hardness.
As such a hardness tester above, a hardness tester is known in which electromagnetic force (force motor) is employed in a mechanism that applies a test force to an indenter to allow selection of a desired test force (refer to Japanese Patent No. 4942579, for example). When the electromagnetic force is employed in the mechanism that applies the test force, a lever system is employed. Thus, when the indenter is pressed into a sample, a relative position changes between a coil and a magnet in a test force applier that generates the electromagnetic force, thus leading to a reduction in magnetic flux density and thus in test force. A conventional hardness tester therefore incorporates a test force correction function to address the reduction in the test force associated with the change of the relative position between the coil and the magnet.
In the conventional hardness tester, however, current flows in the coil to generate the test force. Thus, heat cannot be prevented from being generated in the test force applier. With heat generated in the magnet of the test force applier, the magnetic flux density is reduced, and thus the test force is reduced. In particular, when a large test force (for example, 0.3 to 2 kgf) is generated, a large current (for example, 0.195 to 1.3 A) flows in the coil. Thus, excessive heat is generated in the test force applier, leading to a substantial reduction in the test force.